- EIGRP
- IPv6 Routing: EIGRP Support
- EIGRP MIB
- EIGRP MPLS VPN PE-CE Site of Origin
- EIGRP Nonstop Forwarding Awareness
- EIGRP Nonstop Forwarding
- EIGRP IPv6 NSF/GR
- EIGRP Prefix Limit Support
- EIGRP Support for Route Map Filtering
- EIGRP Route Tag Enhancements
- BFD Support for EIGRP IPv6
- EIGRP Loop-Free Alternate Fast Reroute
- Add Path Support in EIGRP
- EIGRP Wide Metrics
- EIGRP/SAF HMAC-SHA-256 Authentication
- IP EIGRP Route Authentication
- EIGRP IPv6 VRF-Lite
- EIGRP Stub Routing
- EIGRP Support for 6PE/6VPE
- EIGRP Over the Top
- EIGRP OTP VRF Support
- EIGRP Classic to Named Mode Conversion
- EIGRP Scale for DMVPN
- EIGRP IWAN Simplification
- Finding Feature Information
- Prerequisites for Add Path Support in EIGRP
- Restrictions for Add Path Support in EIGRP
- Information About Add Path Support in EIGRP
- How to Configure Add Path Support in EIGRP
- Configuration Examples for Add Path Support in EIGRP
- Additional References for Add Path Support in EIGRP
- Feature Information for Add Path Support in EIGRP
Add Path Support in EIGRP
The Add Path Support in EIGRP feature enables hubs in a single Dynamic Multipoint VPN (DMVPN) domain to advertise multiple best paths to connected spokes when the Enhanced Interior Gateway Routing Protocol (EIGRP) is the routing protocol between the hubs and the spokes. This module provides information about the Add Path Support in EIGRP feature and explains how to configure it.
- Finding Feature Information
- Prerequisites for Add Path Support in EIGRP
- Restrictions for Add Path Support in EIGRP
- Information About Add Path Support in EIGRP
- How to Configure Add Path Support in EIGRP
- Configuration Examples for Add Path Support in EIGRP
- Additional References for Add Path Support in EIGRP
- Feature Information for Add Path Support in EIGRP
Finding Feature Information
Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the feature information table.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Prerequisites for Add Path Support in EIGRP
All interfaces in an Enhanced Interior Gateway Routing Protocol (EIGRP) topology are by default configured with the next-hop-self command. This command enables EIGRP to set the local outbound interface as the next-hop value while advertising a route to a peer, even when advertising routes out of the interface on which the routes were learned. This default EIGRP behavior may interfere with the add-pathscommand that helps configure the Add Path Support in EIGRP feature. Therefore, before you configure this feature on a hub device in a Dynamic Multipoint VPN (DMVPN) domain, you must disable the next-hop-self command that is configured on the hub interface that connects to spokes in the DMVPN domain.
Restrictions for Add Path Support in EIGRP
The Add Path Support in EIGRP feature can be enabled only in Enhanced Interior Gateway Routing Protocol (EIGRP) named mode configurations.
The variance command should not be configured when the Add Path Support in EIGRP feature is enabled. The variance command alters the metrics of routes in an EIGRP topology, thereby enabling EIGRP to balance traffic among desired paths. Therefore, if you configure the variance command on a hub device, the command may interfere with the configuration of this feature.
Information About Add Path Support in EIGRP
EIGRP Add Path Support Overview
In most Dynamic Multipoint VPN (DMVPN) domains, two or more spokes are connected to the same LAN segment. These spokes connect to more than one hub (for hub redundancy) through different service providers (for service-provider redundancy). In a single DMVPN domain, a hub connects to all spokes through one tunnel interface. In Enhanced Interior Gateway Routing Protocol (EIGRP) topologies, when a hub has more than one path (with the same metric but through different spokes) to reach the same network, both paths are chosen as best paths. However, by default, EIGRP advertises only one path as the best path to connected spokes. With the implementation of the Add Path Support in EIGRP feature, hubs in an EIGRP-DMVPN domain can advertise up to four additional best paths to connected spokes, thereby allowing load balancing and path redundancy. This feature supports both IPv4 and IPv6 configurations.
How Add Path Support in EIGRP Works
Spoke-1 and Spoke-2 are connected to a LAN with the network address 192.168.1.0/24. Both these spokes are connected to both the hubs through two different service providers, and hence, these spokes advertise the same LAN network to both hubs. Typically, spokes on the same LAN advertise the same metric; therefore, based on the metric, Hub-1 and Hub-2 have dual Equal-Cost Multipath (ECMP) routes to reach network 192.168.1.0/24. However, because EIGRP is a distance vector protocol, it advertises only one best path to the destination. Therefore, in this EIGRP-DMVPN domain, the hubs advertise only one route (for example, through Spoke-1) to reach network 192.168.1.0/24. When clients in subnet 192.168.2.0/24 communicate with clients in subnet 192.168.1.0/24, all traffic is directed to Spoke-1. Because of this default EIGRP behavior, there is no load balancing on Spoke-3 and Spoke-4. Additionally, if Spoke-1 fails or if the network of Service-Provider 1 goes down, EIGRP must reconverge to provide connectivity to 192.168.1.0/24.
The Add Path Support in EIGRP feature enables EIGRP to advertise up to four additional paths to connected spokes in a single DMVPN domain. If you configure this feature in the example topology discussed above, both Spoke-1 and Spoke-2 will be advertised to Spoke-3 and Spoke-4 as best paths to network 192.168.1.0, thereby allowing load balancing among all spokes in this DMVPN domain.
How to Configure Add Path Support in EIGRP
Configuring IPv4 Add Path Support on a Hub
1.
enable
2.
configure
terminal
3.
router
eigrp
virtual-name
4.
address-family
ipv4
autonomous-system as-number
5.
af-interface
{default
| interface-type interface-number}
6.
no next-hop-self
[no-ecmp-mode]
7.
add-paths
number
8.
end
9.
show
running-config
DETAILED STEPS
Configuring IPv6 Add Path Support on a Hub
1.
enable
2.
configure
terminal
3.
ipv6
unicast-routing
4.
router
eigrp
virtual-name
5.
address-family
ipv6
autonomous-system as-number
6.
af-interface {default
| interface-type interface-number}
7.
no next-hop-self
[no-ecmp-mode]
8.
add-paths
number
9.
end
10.
show
running-config
DETAILED STEPS
Configuration Examples for Add Path Support in EIGRP
- Example: Configuring IPv4 Add Path Support on a Hub
- Example: Configuring IPv6 Add Path Support on a Hub
Example: Configuring IPv4 Add Path Support on a Hub
Device(config)# router eigrp name Device(config-router)# address-family ipv4 autonomous-system 10 Device(config-router-af)# af-interface tunnel 0 Device(config-router-af-interface)# no next-hop-self no-ecmp-mode Device(config-router-af-interface)# add-paths 4 Device(config-router-af-interface)# end
Example: Configuring IPv6 Add Path Support on a Hub
Device(config)# ipv6 unicast-routing Device(config)# router eigrp name Device(config-router)# address-family ipv6 autonomous-system 10 Device(config-router-af)# af-interface tunnel 0 Device(config-router-af-interface)# no next-hop-self no-ecmp-mode Device(config-router-af-interface)# add-paths 4 Device(config-router-af-interface)# end
Additional References for Add Path Support in EIGRP
Related Documents
Related Topic |
Document Title |
---|---|
Cisco IOS commands |
|
EIGRP commands |
|
EIGRP FAQ |
|
EIGRP technology white papers |
Technical Assistance
Description |
Link |
---|---|
The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password. |
Feature Information for Add Path Support in EIGRP
The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Feature Name |
Releases |
Feature Information |
---|---|---|
Add Path Support in EIGRP |
Cisco IOS XE Release 3.8S |
The Add Path Support in EIGRP feature enables a hub in a single Dynamic Multipoint VPN (DMVPN) domain to advertise multiple paths to connected spokes when the Enhanced Interior Gateway Routing Protocol (EIGRP) is the routing protocol between the hub and the spokes. The following command was introduced or modified: add-paths. |